Oracle successfully executes the query and simply ignores the temporal validity clause. If someone accidentally drops your time dimension your application won’t notice and you get wrong results all the time until you have to analyze it because it became an issue (which will probably be very soon).

In my opinion the correct behaviour in this situation would be returning an error, as it is the case when you have an already existing time dimension on the table but use a non-existing one in the query. I already filed a bug in MOS to ask whether this is a bug or a design decision and I will keep this post updated on the outcome.